The present invention relates to a sound volume controlling apparatus suitable for use in telephone systems or audio systems, and more specifically to a sound volume controlling apparatus provided with sound volume controlling keys for increasing or decreasing sound volume when depressed.
A sound volume controlling apparatus incorporated in a telephone set to which receives speech sound or a ringing sound includes sound volume "UP" and "DOWN" keys. In the above-mentioned apparatus, whenever the "UP" key is depressed, sound volume increases stepwise, beginning from the key depression moment, at a constant rate as shown in FIG. 1. On the other hand, whenever the "DOWN" key is depressed, sound volume decreases stepwise, beginning from the key depression moment, at the constant rate.
A problem exists in the above-mentioned apparatus, however, because sound volume starts to increase or decrease the instant that the "UP" or "DOWN" key is depressed, even when the user or something touches these keys erroneously. Thus, even if erroneously depressed, the sound volume keys cause the sound volume inevitably change.